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Posted: 11/22/2008 9:16:46 AM EDT
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Fails to chamber the next round (sometimes).
Jams while feeding (sometimes). When the mag is empty (after manual feeding almost evry round) sometimes the bolt is held open, but the bolt catch is catching the front of the bolt carrier. I believe the bolt is not going all the way back, but am not sure. It always ejects the spent casing. Used about 10 new USGI mags that work fine in other AR's. Any ideas? Thanks for the help. |
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Ammunition used?
Is the gas key binding on the gas tube? It sounds like the rifle is short cycling. The bolt carrier isn't receiving enough gas pressure to fully cycle. As far the bolt catch goes, the magazine when empty locks the bolt to the rear, to help make the operator aware he/she is out of ammunition. This sounds too obvious, so maybe you are referring to something different? BCM makes superior uppers, so I wouldn't blame the upper just yet. Clean the chamber, and gas tube. Use high quality ammunition, and if this persists seek the guidance of a gunsmith. |
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Ammunition used? Is the gas key binding on the gas tube? It sounds like the rifle is short cycling. The bolt carrier isn't receiving enough gas pressure to fully cycle. As far the bolt catch goes, the magazine when empty locks the bolt to the rear, to help make the operator aware he/she is out of ammunition. This sounds too obvious, so maybe you are referring to something different? BCM makes superior uppers, so I wouldn't blame the upper just yet. Clean the chamber, and gas tube. Use high quality ammunition, and if this persists seek the guidance of a gunsmith. Yes, I'm reffering to the bolt catch. The bolt catch is catching the face of the bolt carrier and not the bolt. I think it's short stroking. If so, what's the fix for this drilling the hole larger? |
| Does it function with other ammo? Is the bolt carrier group new or used? Are the rings well oiled on the bolt if new? What buffer? Put oil in the little holes on the side of the BCG. If it cycles a few times and stops you have worn rings or a scored carrier. If you have another BCG try it. It's the ammo, to heavy a buffer( for the ammo), or the BCG in that order. |
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I doubt it's the ammo. This batch works in the other guns. I have another brand new BCG. If I put it in and it works then the problem is the BCG (and I'll send it back). If the new BCG doesn't work, what else could be the problem? Thanks again for the help. First off. NO NO NO NO NO With the Drill. BAD drill. Bad. Sit drill. Sit. Good Drill. Bravo Co. is some good folks to work with. Assuming that it is the gas port that is the problem, you should send it back to them. They'll take care of you. Now, there's a good chance it's not the gas port. If it works with the new BCG, then yes I'd send the other BCG back. Check it at the range first. Check also your gas tube under the handguards. Is it tight and looking right? It doesn't happen often, but they can be defective as any other product. Tex78 |
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Quoted: Correct, standard pinned, not after market. Would you recommend grabbing the new BCG and head back to the range? I really doubt it’s the bolt carrier. The only part of the carrier that could affect the rifles cycling is the gas key. You might want to check the gas passage through the key, and into the carrier by running a pipe cleaner down through it. |
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Correct, standard pinned, not after market. Would you recommend grabbing the new BCG and head back to the range? I really doubt it’s the bolt carrier. The only part of the carrier that could affect the rifles cycling is the gas key.
You might want to check the gas passage through the key, and into the carrier by running a pipe cleaner down through it. Im pretty sure the bolt is also a crucial part of the cycle of an AR. Gas flows through the key into the gas chamber, this gas then pushes the bolt back, rotating it by means of the cam pin. So if there is something gumming up the works with the bolt rings, or even the cam pin, this could cause cycling problems. Thats what I would check too. |
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You have to approach trouble shooting cycling problems when suspecting short stroking, by starting at the beginning of the system. This is the standard with the Principles Of Trouble shooting ANY mechanical system.
1) Is the ammo under powered? 2) Are you really experiencing short stroking? Have you tried the one round/bolt hold open check? 3) Is the barrel gas port under sized, partially blocked? 4) Is the gas tube port in the FSB under sized, partially blocked? 5) Is the gas tube port under sized, partially blocked? 6) Is the gas tube it self partially blocked? 7) And finally, is the carrier key partially blocked? If all this checks out good, then I would start looking at a mechanical reason why the bolt and carrier are not cycling full travel. 1) Carrier gas key to gas tube contact? 2) Obstructed lower receiver extension? 3) Buffer spring too long? Over powered? 4) Buffer pad roll pin walking? 5) Incorrect length stock screw on A1 or A2 stock equipped rifles. 6) Insufficient lube? I may have left a few out, but this ought to get you on the right path. Just use the process of elimination, start at the beginning of the system, and work your way back. |
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Quoted: Quoted: Quoted: Correct, standard pinned, not after market. Would you recommend grabbing the new BCG and head back to the range? I really doubt it’s the bolt carrier. The only part of the carrier that could affect the rifles cycling is the gas key. You might want to check the gas passage through the key, and into the carrier by running a pipe cleaner down through it. Im pretty sure the bolt is also a crucial part of the cycle of an AR. Gas flows through the key into the gas chamber, this gas then pushes the bolt back, rotating it by means of the cam pin. So if there is something gumming up the works with the bolt rings, or even the cam pin, this could cause cycling problems. Thats what I would check too. I’m talking GAS related probable causes, not mechanical. I’m well aware of how the AR15 functions. |
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I wrote this some time ago as a to provide a very basic guide http://www.10-8forums.com/ubbthreads/showflat.php?Cat=0&Board=Bravo&Number=55870&page=0&fpart=all Basic Trouble Shooting Tech Info for the AR15 Platform This is some very basic information on troubleshooting and is not meant to be completely comprehensive. However it generally will address most of the common issues associated with the AR15 series of rifles. This information assumes you have a working knowledge of an AR15 type rifle and practice safe firearms handling. Short stroking (Failure to cycle) Short stroking on an AR rifle is when the bolt carrier group does not cycle far enough to the rear to be able to strip a round from the magazine and feed it into the chamber. After firing a round, you will notice that the bolt is closed on an empty chamber, thereby forcing you to manually cycle the rifle (with charging handle) to feed the next round. This occurs when there is an issue with the gas system. To see if you have a short stroking problem and not a “Failure to Feed” problem, please perform this test first (assuming your bolt catch and magazine is functioning properly). Insert one round into a magazine that you know to be performing well. Insert the magazine into the magazine well, pull the charging handle to the rear, and then release the charging handle to load the round into the chamber. Safely discharge that round. After the round has been fired, the bolt should automatically be locked to the rear by the bolt catch and the empty magazine. If the bolt is closed on the empty chamber, then it did not travel far enough to the rear to be held by the bolt catch, and your rifle has short stroked. Short stroking is a symptom of a problem with the gas system in the rifle. There are 7 parts of the AR gas system. In the upper receiver group, you have the barrel (gas port), front sight base, and gas tube. In the bolt carrier group you have the gas key, the carrier, the bolt, and the gas rings. Assuming the rifle was running correctly previously (in the exact configuration it is currently). The following is a basic trouble-shooting checklist. 1) Ammo issue? Commercial ammo does not run as hot as Milspec ammo, and some lots of commercial ammo may not be strong enough to cycle the weapon. Try a completely different type of ammo. If the weapon works correctly, then you may have some bad ammo. This is becoming a more common problem with some of the low cost imported ammo, especially with carbines that use milspec sized gas ports. 2) Lube and clean the rifle. Pull out your GI manual and properly clean the weapon. As a note, a little bit of dirt and carbon should not stop the proper cycling of your rifle. 3) Check the carrier (gas) key. If the carrier key is loose, the gas system will not hold enough pressure to fully cycle the weapon. Try a different carrier that you know to be working in another properly functioning weapon. If the weapon runs well with the other carrier, you may have an issue with your carrier key. The carrier key bolts should not be loose. It should be staked from the factory. Check to make sure the bolts securing the key did not rotate past the staking. The bolts should be torqued to 35-40 in/lbs. 4) Check the gas rings. (or just go ahead and change them – they are very inexpensive) Mythbuster: The gaps in the gas rings do not need to be staggered. I know we were all taught otherwise in recruit training, and yes I know it says they must be staggered in the GI manual. But this is a myth. As a note; it will not hurt the system to stagger the gaps in the rings, but if this single change makes the difference – you need new gas rings ASAP. Inspect the rings, make sure there are 3 of them, and that they are installed properly. Disassemble the carrier group, insert the bolt into the carrier, and hold the carrier vertically in the air. The bolt should not fall out of the carrier. 5) Change the gas tube. Failure to Feed A failure to feed initially looks similar to a short stroking problem. A round is fired, a spent case is extracted and ejected, and the bolt is closed on an empty chamber. The difference with a failure to feed is that the bolt did travel far enough to the rear to chamber a round, but it is still closed on an empty chamber. Generally speaking, a failure to feed is most often caused by a defective magazine (specifically a problem with the feed lips). You might also notice 2 dents on the top casing that is still loaded in the magazine from bolt over-ride. The solution is to replace the magazine. USGI magazines are class 9 expendable and should be replaced when defective. Failure to Extract This is signified by a spent casing stuck in the chamber, not fully extracted from the chamber, or one spent casing and one live round being stuck in the chamber. (Sometimes one spent casing and one live round stuck in the chamber is called a “double feed”, but a double feed is technically 2 live rounds stuck in the chamber) Assuming the weapon ran correctly before and it is in the same configuration, this is generally an indication of a failure of the extractor assembly. The extractor assembly is made up of the extractor, the extractor spring, and the extractor buffer insert. First remove the extractor and inspect it for crack, chips or deformations. If it has any, then replace the extractor. The commercial market also has seen some MIM extractors, so if your extractor has any MIM/casting type markings then replace it. The most common wear point for the extractor is in the spring. As these springs wear out they become weak and do not have the proper tension to extract correctly. Replace the extractor spring and extractor rubber insert. Be careful to order the correct part specific to your weapon. There are stronger extractor springs on the market made to address the increased pressure that the carbine systems run under. These are recommended. Also the rubber insert you replace should be replaced with a black rubber insert. The original M16A2s had a blue insert. A stronger black insert was introduced for the M4 and is an improvement over the blue and is good to go in both rifles and carbines. Another fix is the D-fender rings or O-rings found on the market. Install them over your extractor spring. This was a standard upgrade for the M4A1s done by Crane Industries for SOCOM. Now assuming you have these issues on a newly built weapon, then you may need to go past the above advise and look at some other areas. Issues like this are most commonly seen on shorter barreled AR15s. With a shorter barreled AR (generally 14.5”, 11.5”, 10.5”, 10.3”) you have about twice the pressure in the system with less dwell time (shorter than 14.5”) and a faster unlock time. One of the issues that needs to be addressed is slowing the cycle rate of these shorter barreled carbines. This is done in part by the addition of a tungsten weighted buffer. The M4 carbine runs a H-buffer and the M4A1 carbine runs an H2 buffer. There are also H3 buffers that see some use (most often in Commandos). Also stronger recoil springs can provide some aid. If all else fails you may need to look at gas port size and/or confirm that the chamber is not cut too tight. |
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Correct, standard pinned, not after market. Would you recommend grabbing the new BCG and head back to the range? I really doubt it’s the bolt carrier. The only part of the carrier that could affect the rifles cycling is the gas key.
You might want to check the gas passage through the key, and into the carrier by running a pipe cleaner down through it. Im pretty sure the bolt is also a crucial part of the cycle of an AR. Gas flows through the key into the gas chamber, this gas then pushes the bolt back, rotating it by means of the cam pin. So if there is something gumming up the works with the bolt rings, or even the cam pin, this could cause cycling problems. Thats what I would check too. I’m talking GAS related probable causes, not mechanical. I’m well aware of how the AR15 functions.
Sorry Quib  . I actually didnt noticed it was you i was replying to. I mean no disrespect. 
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Quoted: I wrote this some time ago as a to provide a very basic guide http://www.10-8forums.com/ubbthreads/showflat.php?Cat=0&Board=Bravo&Number=55870&page=0&fpart=all Good write-up, it hits some points I over looked in my brief TSing run-down.  |
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First, thanks for all the input from everyone.
Second, I was in no way downing BCM or their products. Third, I went back to the range and... The ammo I was using was Privi Partisan from Serbia - M855/SS109. This ammo worked fine in my other BCM and CMMG. I used some Federal XM193 (brown box) in the BCM and had much better success. Come to find out, the few problems I was still having turned out to be one bad mag that was continuously being cycled through. Once I took that mag out of the equation, the upper ran flawlessly on the M193. I then loaded a few mags with one round each. Some with the M855 and some with the M193. When a mag with 193 worked I'd put an 855 in and then it would fail 100% of the time. So... the upper works with M193, but not the M855. My other BCM, CMMG and LMT 10.5" work fine with the M855. Is it because the rifle is new and needs to be broken in? When alternating between the two rounds, the 855 was noticably weaker. It appeared that the cycling rate was too slow and allowing the bolt catch to catch the front of the bolt carrier face. Does this sound right? The only mag I have with a black follower (Okay Ind.) was the only one I had problems with. Any coincidence? Thanks again for all of your help. |
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So it sounds like a combination of rifle break-in time and under powered ammo.
Keep her lubed up well, give her time to break-in, and keep shooting the ammo she likes best. Eventually when she gets broke in, you might try going back to the weaker ammo just to see if cycling has improved. |
| If you want to break it in without wasting ammo you can take the upper off and hold it at 45 degrees. Grab the BCG and pull it to the read and let it drop. It should go into battery. If not lube it up and continue about 20 to 50 times. If it still is rough then the gas tube needs adjustment. I had to tweak the barrel nut ever so slightly on my last BCM M4 to get the BGC to drop in smoothly. The gas tube was rubbing on one side which is a common problem with all carbines due to the short gas system. It's also difficult for the manufacture to check since it may test out fine with the BGC they use for testing. I understand why BCM, LMT and others sell the upper without a BGC but if it were me I would only sell a complete upper with BGC that had been test fired as an assembly. This would insure every upper sent out would be 100%. |
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If you want to break it in without wasting ammo you can take the upper off and hold it at 45 degrees. Grab the BCG and pull it to the read and let it drop. It should go into battery. If not lube it up and continue about 20 to 50 times. If it still is rough then the gas tube needs adjustment. I had to tweak the barrel nut ever so slightly on my last BCM M4 to get the BGC to drop in smoothly. The gas tube was rubbing on one side which is a common problem with all carbines due to the short gas system. It's also difficult for the manufacture to check since it may test out fine with the BGC they use for testing. I understand why BCM, LMT and others sell the upper without a BGC but if it were me I would only sell a complete upper with BGC that had been test fired as an assembly. This would insure every upper sent out would be 100%. What does pull it to the read mean? On both of the BCM uppers I purchased the gas tube had to be adjusted. Thanks KJB. |
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At this point... this upper fires: LC M193, Privi M193 & Federal .223 55GR and the bolt locks to the rear on the last round without a problem.
It will fire the Privi M855 with no problems until the last round in the mag. Everytime without fail, the bolt catch catches the front of the bolt carrier, not the bolt. Why would this happen on only the last round? It happens with all the mags, not just one. I'm having a hard time justifying keeping it. |
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At this point... this upper fires: LC M193, Privi M193 & Federal .223 55GR and the bolt locks to the rear on the last round without a problem. It will fire the Privi M855 with no problems until the last round in the mag. Everytime without fail, the bolt catch catches the front of the bolt carrier, not the bolt. Why would this happen on only the last round? It happens with all the mags, not just one. I'm having a hard time justifying keeping it. May I draw the conclusion the rifle performs flawless using good ammo ? I plan to order an upper this week, Bravo is top of the list. (No, I'm not thinking your rifle) Just wish your story has a happy ending. Did you try it with the other BCG you say you have ? |
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If you want to break it in without wasting ammo you can take the upper off and hold it at 45 degrees. Grab the BCG and pull it to the read and let it drop. It should go into battery. If not lube it up and continue about 20 to 50 times. If it still is rough then the gas tube needs adjustment. I had to tweak the barrel nut ever so slightly on my last BCM M4 to get the BGC to drop in smoothly. The gas tube was rubbing on one side which is a common problem with all carbines due to the short gas system. It's also difficult for the manufacture to check since it may test out fine with the BGC they use for testing. I understand why BCM, LMT and others sell the upper without a BGC but if it were me I would only sell a complete upper with BGC that had been test fired as an assembly. This would insure every upper sent out would be 100%. Just curious ... Is it "imperative" that this test be conducted without the charging handle in place - or does it not matter ? |
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If you want to break it in without wasting ammo you can take the upper off and hold it at 45 degrees. Grab the BCG and pull it to the read and let it drop. It should go into battery. If not lube it up and continue about 20 to 50 times. If it still is rough then the gas tube needs adjustment. I had to tweak the barrel nut ever so slightly on my last BCM M4 to get the BGC to drop in smoothly. The gas tube was rubbing on one side which is a common problem with all carbines due to the short gas system. It's also difficult for the manufacture to check since it may test out fine with the BGC they use for testing. I understand why BCM, LMT and others sell the upper without a BGC but if it were me I would only sell a complete upper with BGC that had been test fired as an assembly. This would insure every upper sent out would be 100%. Just curious ... Is it "imperative" that this test be conducted without the charging handle in place - or does it not matter ? Not really but sometimes a handle can be the issue. |
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